Fuel cell with purge manifold

ABSTRACT

A fuel cell includes an electrode assembly having an electrolyte between an anode and a cathode for generating an electric current and byproduct water. A porous plate is located adjacent to the electrode and includes reactant gas channels for delivering a reactant gas to the electrode assembly. A separator plate is located adjacent the porous plate such that the porous plate is between the electrode assembly and the separator plate. The separator plate includes a reactant gas inlet manifold and a reactant gas outlet manifold in fluid connection with the reactant gas channels, and a purge manifold in fluid connection with the porous plate such that limiting flow of the reactant gas from the reactant gas outlet manifold and opening the purge manifold under a pressure of the reactant gas in the reactant gas channels drives the byproduct water toward the purge manifold for removal from the fuel cell.

BACKGROUND OF THE DISCLOSURE

This disclosure relates to fuel cells for generating electricity.Conventional fuel cells typically include an anode, a cathode, and anelectrolyte between the anode and the cathode for generating an electriccurrent in a known electrochemical reaction between reactant gases, suchas hydrogen and air. The electrochemical reaction produces water as abyproduct. Typically, the water is removed from the cell using anadjacent structure, such as a plate.

One problem associated with such fuel cells is that upon shutdown of thefuel cell, water can remain in the fuel cell. Under cold conditions, thewater may freeze and subsequently inhibit movement of the reactant gasesto the anode and cathode when the fuel cell is restarted. One possiblesolution is to allow the water to drain out of the fuel cell aftershutdown. However, draining the water may take a considerable amount oftime and may require auxiliary pumps or other parasitic power devices.

SUMMARY OF THE DISCLOSURE

An exemplary fuel cell includes an electrode assembly having anelectrolyte between an anode and a cathode for generating an electriccurrent and byproduct water. A porous plate is located adjacent to theelectrode and includes reactant gas channels for delivering a reactantgas to the electrode assembly. A separator plate is located adjacent theporous plate such that the porous plate is between the electrodeassembly and the separator plate. The separator plate includes areactant gas inlet manifold and a reactant gas outlet manifold in fluidconnection with the reactant gas channels, and a purge manifold in fluidconnection with the porous plate such that limiting flow of the reactantgas from the reactant gas outlet manifold and opening the purge manifoldunder a pressure of the reactant gas in the reactant gas channels drivesthe byproduct water toward the purge manifold for removal from the fuelcell.

An exemplary method of managing water removal in the fuel cell includeslimiting flow of the reactant gas from the reactant gas manifold,allowing a flow of the byproduct water through the purge manifold, andestablishing a pressure of the reactant gas in the reactant gas channelssuch that the reactant gas drives the byproduct water toward the purgemanifold for removal from the fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the disclosed examples willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example fuel cell.

FIG. 2 illustrates a perspective view of a cathode separator plate,porous plate, and an electrode assembly of the fuel cell.

FIG. 3 illustrates a view of the cathode separator plate and the porousplate showing the flow of reactant gases during normal operation.

FIG. 4 illustrates a view of the cathode separator plate and the porousplate showing purging of water in the fuel cell.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates schematic, exploded view of selected portions of anexample fuel cell 10. In this example, the fuel cell 10 includes a fuelcell unit 12 that operates in a known manner to generate electricity.For instance, multiple fuel cell units 12 may be stacked in a knownmanner to provide a desired amount of electrical output. However, it isto be understood that this disclosure is not limited to the arrangementof the example fuel cell 10, and the concepts disclosed herein may beapplied to other fuel cell arrangements.

The fuel cell unit 12 includes an electrode assembly 14 located betweena porous plate 16 and an anode separator plate 18. The porous plate 16is located between the electrode assembly 14 and a cathode separatorplate 20.

The electrode assembly 14 may include an electrolyte 22 located betweena cathode 24 and an anode 26. Optionally, a gas diffusion layer 28, suchas a porous or fibrous layer, may be located between the electrodeassembly 14 and each of the anode separator plate 18 and the porousplate 16.

In this example, the porous plate 16 includes reactant gas channels 30for delivering a reactant gas, such as an oxidant (e.g., air), to thecathode 24 of the electrode assembly 14. Likewise, the anode separatorplate 18 may include channels 32 for delivering another reactant gas,such as hydrogen, to the anode 26 of the electrode assembly 14. In thiscase, the anode separator plate 18 also includes coolant channels 34 onthe opposite side of the anode separator plate 18 from the reactant gaschannels 32 for cooling the fuel cell 10.

The porous plate 16 includes pores 40 for facilitating waterredistribution through the fuel cell 10, such as liquid byproduct waterfrom the electrochemical reaction at the electrode assembly 14. Forinstance, the pores 40 may have an average pore radius of 0.1-10micrometers (3.9-394 microinches). Additionally, the porous plate 16 mayhave a porosity that is about 5-50%. The example average pore size andporosity provide the benefit of wicking water away from the electrodeassembly 14 by using capillary forces, for example.

The porous plate 16, the anode separator plate 18, and the cathodeseparator plate 20 may be made of any suitable material for achievingthe given functions. In a few non-limiting examples, the porous plate16, the anode separator plate 18, the cathode separator plate 20, oreach are made from a material including carbon, iron, nickel, chromium,aluminum, titanium, gold, platinum, or combinations thereof.

FIG. 2 illustrates a perspective view of the electrode assembly 14, theporous plate 16, and the cathode separator plate 20. The cathodeseparator plate 20 includes a reactant gas inlet manifold 50 and areactant gas outlet manifold 52 that are fluidly connected with thereactant gas channels 30 of the porous plate 16 such that a reactant gasdelivered through the reactant gas inlet manifold 50 is allowed to flowthrough the reactant gas channel 30 and exit through the reactant gasoutlet manifold 52. A second reactant gas inlet manifold 50 a and asecond reactant gas outlet manifold 52 a may likewise be used to deliverfuel to the reactant gas channels 32 of the anode separator plate 18.The cathode separator plate 20 may also include coolant manifolds 54 forcirculating coolant through the coolant channels 34 of the anodeseparator plate 18.

The cathode separator plate 20 also includes a purge manifold 56 that isin fluid connection with the porous plate 16. For instance, the purgemanifold 56 is adjacent to the porous plate 16 to collect watertherefrom, as will be described below. Optionally, the cathode separatorplate 20 may include a divider 58 that separates the purge manifold 56from porous plate 16. The divider 58 may include channels 59 adjacentone side of the cathode separator plate 20 (i.e., the back side in FIG.2) that extend through the divider between the porous plate 16 and thepurge manifold 56 to facilitate water transport. For instance, watermovement in the plane of the porous plate 16 may be limited because ofpore size. By locating the channels at one side of the cathode separatorplate 20, the channels promote water movement through the thickness ofthe cathode separator plate 20 (i.e., out-of-plane water movement),which is not so limited.

Referring to FIG. 3, the fuel cell 10 may also include an inlet valve 60associated with the inlet manifold 50, and an outlet valve 62 associatedwith the reactant gas outlet manifold 52. For instance, the inlet valve60 may be used in a known manner to control flow of the reactant gasinto the reactant gas inlet manifold 50, and the outlet valve 62 may beused to limit flow of the reactant gas from the reactant gas outletmanifold 52. The flow arrow 66 generally indicate the direction of flowof the reactant gas between the reactant gas inlet manifold 50 and thereactant gas outlet manifold 52 when the inlet valve 60 and the outletvalve 62 are open. Likewise, the reactant gas inlet manifold 50 a andthe reactant gas outlet manifold 52 a may also include valves forcontrolling the flow of fuel between the reactant gas channels 32 of theanode separator plate 18.

The fuel cell 10 also includes a purge valve 64 associated with thepurge manifold 56 for controlling flow through the purge manifold 56 tothe surrounding environment. As illustrated in FIG. 3, the reactant gasflows from the reactant gas inlet manifold 50 toward the reactant gasoutlet manifold 52 when the inlet valve 60 is in an open state, theoutlet valve 62 is in an open state, and the purge valve 64 is in aclosed state.

However, as illustrated in FIG. 4, the outlet valve 62 may be closed andthe purge valve 64 may be opened to purge water from the fuel cell 10upon shutdown, for example. For instance, the outlet valve 62 may be atleast partially closed or completely closed to limit the flow of thereactant gas through the reactant gas outlet manifold 52. The purgevalve 64 may be opened in conjunction with closing of the outlet valve62 such that the reactant gas within the reactant gas channels 30 of theporous plate 16 flows toward the purge manifold 56, as indicated by flowarrows 66, rather than the reactant gas outlet manifold 52. The pressureof the reactant gas in the reactant gas channels 30 drives out water inthe fuel cell 10, such as water within the pores 40 of the porous plate16, water in the gas diffusion layer 28, or water in other locations, tofacilitate avoidance of freezing after shutdown.

In one example, the flow of the reactant gas into the fuel cell 10through the reactant gas inlet manifold 50 may be controlled to purgeany remaining water. For example, the flow may be controlled toestablish an elevated pressure (relative to the surrounding environment)to drive out the water. The pressure may be about 10-200 kPag (1.45-29psi). In another example, the pressure may be about 100-200 kPag(14.5-29 psi) to overcome capillary pressures within the pores 40 of theporous plate 16 and thereby drive the water out from the pores 40. Inthis regard, the fuel cell 10 can be rapidly flushed of the water bypressurizing the fuel cell 10 with the reactant gas. Using the pressureof the reactant gas eliminates waiting for gravitational forces alone toremove the water, and also eliminates the need for using parasiticauxiliary equipment to pump the water out. For instance, the fuel cell10 may be rapidly flushed of the water during, just before, or justafter shutdown.

The purge manifold 56 may be located anywhere on the cathode separatorplate 20. In the illustrated example, the purge manifold 56 is locatedtoward the bottom of the cathode separator plate 20 and below thereactant gas inlet manifold 50 to additionally utilize gravitationalforces to remove the water. In a further example, the cathode separatorplate 20 includes an upper half and a lower half (as indicated at 59when oriented vertically), and the purge manifold 56 is located withinthe lower half to utilize gravitational forces to facilitate removal ofthe water. In other examples, the purge manifold 56 may be at the bottomof the cathode separator plate 20.

U.S. patent application Ser. No. 13/256,326 is hereby incorporatedherein by reference in its entirety.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

What is claimed is:
 1. A fuel cell comprising: an electrode assemblyincluding an electrolyte between an anode and a cathode for generatingan electric current and byproduct water; a porous plate adjacent theelectrode assembly, the porous plate including reactant gas channels fordelivering a reactant gas to the electrode assembly; and a separatorplate adjacent the porous plate such that the porous plate is betweenthe electrode assembly and the separator plate, the separator plateincluding a reactant gas inlet manifold and a reactant gas outletmanifold in fluid connection with the reactant gas channels, and a purgemanifold in fluid connection with the porous plate such that limitingflow of the reactant gas through the reactant gas outlet manifold andopening the purge manifold under a pressure of the reactant gas in thereactant gas channels drives the byproduct water through pores in theporous plate toward the purge manifold for removal from the fuel cell.2. The fuel cell as recited in claim 1, wherein the porous plate isdirectly adjacent the cathode.
 3. The fuel cell as recited in claim 1,further comprising an outlet valve associated with the reactant gasoutlet manifold for limiting flow of the reactant gas through thereactant gas outlet manifold, and a purge valve associated with thepurge manifold for selectively limiting flow of the reactant gas throughthe purge manifold.
 4. The fuel cell as recited in claim 1, wherein theporous plate includes an average pore size of about 0.1-10 micrometers.5. The fuel cell as recited in claim 1, wherein the porous plate has aporosity of about 5-50%.
 6. The fuel cell as recited in claim 1, whereinthe porous plate has a water contact angle of about 0-90°.
 7. The fuelcell as recited in claim 1, wherein at least one of the porous plate orthe separator plate includes a material selected from the groupconsisting of carbon, iron, nickel, chromium, aluminum, titanium, gold,platinum, and combinations thereof.
 8. The fuel cell as recited in claim1, wherein the purge manifold is below the reactant gas inlet manifoldwhen the separator plate is vertically oriented.
 9. The fuel cell asrecited in claim 1, wherein the purge manifold is located in a lowerhalf of the separator plate when the separator plate is verticallyoriented.